Thermal store cycliners - which one/any good?

[Tim]

Hi

*** Preamble *******************************************************

The ongoing wibblings of moving my family in with Dad... [Dad's house is a

3 bedroom bungalow with roof converstion fitted with "evolved" CH, but new boiler - vented type]

As some of the radiator pipework is poorly run (miles of 10mm supplying 2 large double panel rads :-( ) and there's much weirdness in the plumbing due to previous add-ons and random work, I'm going to replace a fair bit of the CH copper.

So, I thought I might as well consider a thermal store cylinder at the same time. Good excuse to have the old cylinder out and rationalise all the odd pipework round the back.

This solves the problem of insufficient hot water pressure upstairs and gets rid of a massive tank in a little room that could be used as decent storage space.

Disclaimer - I've done some basic plumbing on occasion but I'm not upto date with modern practises.

*** Actual research and questions ************************************

Seems like a generally good idea to go for a thermal store system. His incoming mains water pipe was changed recently back to the road to the blue plastic stuff.

Q: would that imply it's 25mm? Looks fairly chunky.

And, Dad already changed the copper that meets this and feeds into the house on the first leg to 22mm. And the mains water pressure is mentally high - though I have yet to take a dynamic pressure reading. So I think the house meets the criteria for such a system.

Q: But - which one? I've been all over the web and found:

McDonald Engineers' ThermFlow - simple cylinder, use 2 external pumps (boiler primary and CH)

Gledhill BoilerMate2000/SysteMate2000 (can't work out what the difference is yet - possible one is direct and the other indirect??) Very poncy design with microprocessor control, 3 pumps (why there's a pump on the mains water circuit I don't know) and lots of sensors to go wrong. Looks pretty though. Expensive at 1200 squids up, but does include the controler and all the pumps in a nice neat housing.

Heatweb - Also looks complicated like the Gledhill, but not as neat.

Albion - simple again, like the McDonalds'.

Q: Would I want direct or indirect? Direct seems simpler - pump the boiler primary through the bulk of the tank and the rads.

*** Final and the ultimate question ***********************************

So - from people that fitted thermal store cylinders: are they any good and which one did you use? Any general theories/opinions also most welcome :-)

Ta very muchly. Timbo

[Grunff]

Probably, could be 32mm.

I have a range 210l thermal store (but used with a plate exchanger, so I'm told that makes it a heatbank ;-). It's very good. I'm very happy, and would buy another one.

I have direct, and it works very well with our oil boiler.

Yes, I think they're great. The large stored capacity means long burn times for the boiler, all the hot water you want, and immediate heating up of the house when the CH kicks in.

[Christian McArdle]

It has significant advantages and disadvantages. The main advantage is that it allows the boiler to reheat the store in a very efficient manner, dumping its full load into the cylinder, rather than relying on an indirect coil that might not be able to transfer as much heat. This is particularly useful if you are running radiators off the store. It also allows the boiler to use a lower flow temperature (good for condensing) as there is no need to provide a temperature differential that a heat exchanger would require. You can run the boiler at 75C, rather than 82-85C.

The main disadvantage is that it doesn't allow sealed pressurised operation of the boiler, a system which has a number of advantages, such as leak detection and protection, pump over prevention, easier filling & flushing, allowing radiators high up, etc.

I have a DPS Pandora heat bank (you refer to these as the "heatweb"). It is an indirect type, as there are likely to be radiators as the highest point in the system, so I wanted sealed pressurised operation. The rads are off the boiler primary, not from the heat bank.

It is absolutely excellent and works entirely as described. It has been fitted for over a year and I still haven't had to top it up (manual fill version). I believe the Gledhill may be technically superior to the model I have. In particular, it is my understanding that the Gledhill varies pump speed to maintain heat bank stratification. However, I haven't in practice found destratification to be a problem as the system never really runs out of hot water.

The biggest test was filling a 750 litre birthing pool to 40C. It managed this in just over 40 minutes, although the outlet temperature did drop to about the required 40C by the time it had completed.

In conclusion, I would definitely fit this type of system again. Although my parent's Megaflo also provides excellent performance, I prefer the easy maintenance of the heat bank.

BTW, I'd avoid the traditional thermal store type devices. I would only choose a model with a plate heat exchanger for DHW operation.

Christian.

[Tim]

Hi Christian,

Thanks for your reply.

That seems a clear choice then, for me (see below).

Longer life for the boiler...

Shouldn't be a problem. Only got rads on 2 floors, with the cylider on the lower floor - I assume that will be OK?

Ah yes - Heatweb stuck in my mind, but they do sell different things - yes it was the Pandora.

I can't make up my mind whether to take the rads off the primary via a 3 way valve or use the heat store to feed them. I suppose that using the heat store will guarantee long boiler burns. But is there a danger that the radiators will deplete the heat from the store? Some pictures indicate that the radiator feed is taken off the lower half of the cylinder, so I presume not??

Was there any particular reason you fed the rads directly from the primary?

Hmm - this idea sounds better than ever :-)

Wow. I don't think that I've had a CH HW system that could run for 40 minutes without going stone cold after 20.

Ah - I did see "heat plate" mentioned.

Thank you very much.

Timbo

[Tim]

Hi again

Follow on question:

Did you use any particularly special controller? I presume one could use a basic timeswitch/room thermostat combo (or zoned set thereof) doing the CH rad pump (and zone valves), with a thermostat on the thermal store doing the boiler control? And couple the primary circuit pump to the boiler control**

** The Gledhill does make special mention of running the pump on for some minutes after the boiler cuts out to be nice to the boiler.

Ta,

Timbo

[Tim]

Flow shouldn't be a problem then :-)

Sounds good. Which type is it - also Pandora? I hadn't yet come across the idea of using an external heat plate exchanger until now...

OK.

I was sort of convinced before (but worried that it might be a "fad" product), but now that people say thay actually work I'm strongly convinced that this is the way to go.

Half expecting someone to suggest I fit a combi instead! ;-/

Many thanks

Tim...

[Christian McArdle]

Yes, but you must specify a model that can be topped up from a roof tank and be vented in the conventional way. The specific DPS Pandora I have wouldn't work, as it requires to be the highest point in the system. This wasn't a problem for me, as I'm not running radiators through it, so it is the only point in the system...

Christian.

[Christian McArdle]

Yes, the radiators are (or will be when I convert the loft) the highest point in the system. This means that they require a sealed pressurised system. It is actually possible to have a sealed pressurised system fed from the heat bank, but this requires 2 additional pumps and an additional plate heat exchanger. The boiler and cylinder are already in the loft and I didn't want additional tanks above, even if they could have been accommodated somehow.

Christian.

[Tim]

Oops - one more poser... Sorry.

I mentioned a while back (not that anyone would be expected to remember) that I was possibly going to use wet underfloor heating in a conservatory (modern B/Regs aside...)

Now, I'd want a lower water temperature for that (at least not 70+).

Is there a good way I can work this into the design at this stage without going to the lengths of using some sort of mixer system?

I can't obviously see one - but I've just discovered since reading various replies that I still don't know half of the options available with thermal store systems. Everytime I read up on the web, there's another product with a slightly differnt way of doing things.

Ta muchly.

Timbo

[Tim]

OK... Sorry for being thick: The header tank's already in the roof and it's staying there (3 ft above the highest rad).

I'd assumed that the thermal store water + boiler primary were generally pressuried by the header tank (though I did notice that your Pandora is locally filled through a little plug in the top of the cylinder, which I hadn't expected?)

In other words, I though that the termal store system wasn't dissimilar to the way that a conventional HW cylinder is pressurised by the CW tank in the loft. So I hadn't actually foreseen a problem, as long as the rads were below the header tank level.

Is this an area which thermal stores vary a lot in, and does "sealed pressurised system" mean "fed from a header tank in the loft"?

Sorry again for sounding like a bit of a plank. :/

Timbo

[Grunff]

I don't actually know - it came from Range, as did the flow switch which drives it.

Two combis - you always need two.

[Christian McArdle]

No, my system is bog standard S-Plan-Plus off the boiler. Standard 2 channel programmer, with both CH and HW to always on. 4 zones, 3 heating (to be expanded to 5) and 1 for the heat bank. All heating zones have programmable thermostats.

Had I run the radiators through the heatbank, I would have used a slightly unusual control system, due to the radiator positioning requirements I have. Basically, I would have a second plate exchanger pumped loop. The other side of this exchanger would have been a sealed pressurised circuit, subdivided using S-Plan-Plus zone valve, pump and controls to the radiator zones. This gives the advantage of limited leakage, leakage detection, high mounted radiators and pressure fill, which might as well be used downstairs and well as in the loft conversion.

The gravity primary circuit would then only be used within the heat bank, the DHW and CH plate exchanger loops and the boiler (although indirect would also work, assuming a coil that matches the boiler's output).

Christian.

[Christian McArdle]

Or 2 multipoint heaters instead.

Christian.

[Christian McArdle]

Note also that it is worth connecting up 2 vertically separated cylinder thermostats to create a very high hysterysis network. This way, you get long efficient burns and keep the primary cold most of the time, avoiding losses there.

Christian.

[Christian McArdle]

Yes, and you would need to use a similar system in your setup.

However, in certain circumstances (such as mine), you can take advantage of the fact that the water goes nowhere to remove the expense, space and inconvenience of having the header tank. In your case, I don't think you can and you need a conventional vented tank arrangement.

No, it means a sealed circuit with no vent, filled from a hose from the mains, with a pressure gauge, pressure relief valve and expansion pressure vessel. There is no need for there to be a boiler in circuit to have one. You can run a sealed pressurised circuit from the heat bank, with an additional heat exchanger, but it adds to complexity.

Christian.

[Christian McArdle]

Nah. Put it a mixer system. You need fine specific temperature control for that application. You might get away with putting the mixer (and pump) near the heat bank (presumably in some sort of airing cupboard), rather than trying to find space near the floor in question, although with all these circuits, pumps, valves etc., it's going to look like the engines of the space shuttle before long. Make sure you document what all the bits do!

Christian.

[Tim]

Brilliant - that means I understand it now. Thanks again.

I'm all for simplicity :)

Timbo

[IMM]

A thermal store has an inegral DHW coil. A heat bank a DHW plate heat exchanger fed by a pump.

The Boilermate is an "integrated" store, that is the CH and DHW are run off the store. The Sytemate has the CH run direst from the boioer with the store being DHW only.

All the controls/pumps etc in inside the neat casing in both. The control systems are superb in both. The are not direct. I have a Systemate. They are best available and state-of-the-art. They are self adaptive in that they learn the boilers behaviour. They modulate the DHW pump speed to suit the outlet temperature. A pump is on the mains water circuit, well it is on the primary circuit, to pump heat into the plate heat exchanger. They are also very reliable too.

Also look at

Flowmax, which is a a well priced heat bank.

Best have a direct "integrated" heat bank.

But expensive.

Yep.

[IMM]

The Pandora is a DHW only heat bank.

[IMM]

Pressurised thermal stores, where the cylinder is pressurised like an unvented cylinder, are available.